The Microbiology Of Maggots Used In Angling Biology Essay

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Maggots breathe from the anterior end of their body to get oxygen as they burrow through tissue. They bury with the help of two sharp digging hooks. Maggots have a standard development i.e. egg-larva-pupae. The developmental stage can be determined by the length of the maggots. Maggots grow at an increased rate with higher temperature.(Giangiuliani et al. 1994)

Maggots are short in proportion to its thickness and it's smaller at the two ends than in the middle. There is line of dots on the body of maggots; these are the mouths of air canals which serve as a lung. They have smooth skin and are commonly of light cream colour.(Schoofs et al. 2009)

Some of them have tails for the motion in the water. The movement of maggots with feet is a mixture of crawling and walking. The crawling motion is an alternate elongation and contraction of one half of the length of the body. First, the front half lengthen and stretch forward while the following half is contracted and vice versa. The walking is performed by a successive motion of each pair of feet that support these alternate contractions and elongations of a body making head and tail alternately fixed.(Schoofs et al. 2009)

Female flies can place around 500 white eggs in numerous of groups of around 75 to 150. The lengths of these eggs are approximately 1.2 mm. It takes about 24 hours for the eggs to be hatched by larvae known as squats (Singh and Vardanis 1984). The main source of food for consumption of maggots is generally dead organic material like decomposing garbage or faeces. These legless creatures are pale in colour and grow 3-9 mm in length. Larvae stage lasts no less than a week before they crawl to a dry cool place due to their transformation into reddish brown pupae which reach up to 8 mm in length. The mature flies then come out of the pupae. This whole biological process of physical development after the larvae's birth is called 'complete metamorphoses'. The life of adult flies is between 2-4 weeks or even longer under controlled laboratory conditions. The growths of flies come to an end after coming out of the pupae. The small size of some flies does not indicate their growing stage, because at this point flies do not grow up any more, but of course it is the result of inadequate consumption and lack of food during the larval phase. (Bennet S.M. 2008)

Some female flies become ready to mate after 36 hours of emerging from the pupae. She is then mounted and inject with sperm by a male from behind. The duration of mating lasts from few seconds to few minutes and the female stores the sperm to frequently produce eggs. The males' job is to protect a certain territory to make sure no other flies or insects tress pass the area and also to try and mount the female trespassers. (Bennet S.M. 2008)

Figure 2. male and female house fly mating

Just like other insects flies too depend on the warm temperature. The warmer the environment, the more active and faster they are in their development and vice versa. (Bennet 2008)

Figure 3. The life cycle of a common house fly

1.2.2. Bluebottle flies (Calliphora vomitoria) life cycle

Bluebottle flies are a little longer than normal house flies, around 10-14 mm in length. They are blue colour as the name suggests, with dull gray head and thorax, red eyes, black legs and antenna, clear wings and a body covered with bristle.(Wooldridge et al. 2007)

The eggs of blue bottle fly is placed by a female usually as the same place as her consumption area which could be either rotting meat, garbage, and, or faeces. Just like the house fly larvae (maggot), the larvae of blue bottle fly known as Calliphora larvae is also pale-whitish. As soon as these maggots emerge from their eggs, they begin to consume on the surrounding dead or decaying organic material. After few days of consuming, the larvae are fully grown and ready to wrap themselves into thick brown cocoons in a dry cool area where they can stay in for two weeks before emerging from it as an adult fly. Similar to housefly and other insects, the adult blue bottle flies and pupae hibernate during winter, and waken up by warmer temperature when they can be active again in mating, laying eggs. These flies get involved in the activities such as pollinating of some flowers. (Kurashi 2008)

Figure 4. The life cycle of blue bottle fly

1.2.3. Green bottle (L. Sericata) life cycle

The female fly lays a bunch of eggs in an injured area, a corpse (dead body), or in necrotic (dead tissue) or decomposing tissue. The larvae of green bottle known as pinkie hatch from their eggs 8-10 hours after being placed in a warm damp area; however this process could be delayed to three days in a cooler weather condition. The female fly can lay 130 to 172 eggs. The larvae are again pale-whitish. They are 10-14 mm in length. The larva consumes on the dead or decomposing tissue approximately for 3-10 days. This would change as the temperature increases or decreases. During this length of time, the larva goes through 3 larval stages. In the cool temperature of 16oC the first level of larva phase lasts about 53 hours, the second phase, 42 hours, and finally the third and the last phase will take 98 hours to fulfil this part of their life cycle. If the temperature increased to 27oC, the 1st stage would take 31 hours whilst the second stage lasts 12 hours and the 3rd stage will last 40 hours to achieve this particular life cycle. In the 3rd larva stage, the larva will move onto soil to pupate for 6 to 14 days. This will again change if the temperature is lower, and if it is in winter time, they can stay in the soil until the temperature of the soil increases again. Following the transformation of the pupa, the adult fly comes out from the soil and feeds on dead and decomposing tissue. It will take the mature flies two weeks until they begin to lay eggs. The whole duration of the life cycle of the blue bottle fly is between two to three weeks; however this could be reduced during summer time when the temperature is higher which will consequently lead to the more activity of the fly is at its most. There are normally 3 to 4 generations of L. sericata during each year. (Merih 2008)


Figure 5.The life cycle of a green bottle fly. (2006)

1.3 Human Infection and Medical Importance

Flies are commonly developed in unsanitary areas and manures in farms. The most common type of fly found around these areas is the house flies, also known as Musca domestica, scientifically. The major concerns with these flies are that it does not produce damage directly. They transmit pathogens (viruses, fungi, bacteria, protozoa and nematodes). (Fotedar et al. 1992) The pathogenic organisms are transferred by flies from sewages, unclean areas and wastes onto their mouthparts, via their feces and vomitus and then to human or food.

One of the specific problems is the movement of flies from the animal feces to the food soon to be consumed by the human. Moreover, flies can contain the pathogens consumed from unclean or microbe infested area in its mouthparts or alimentary canal for several days, which are transmitted through regurgitation or defecation (Fotedar et al. 1992). Critical health problems can arise if there are food stalls, hospitals or meat market nearby in areas where proper plumbing is necessary such as open latrines or an open drainage.

Table 1. Following are the few commonly transmitted pathogens by the flies: 




Rod shaped bacteria that cause diarrhoea.


Rod shaped bacteria that cause food poisoning.


Rod shaped bacteria that cause urinary tract infection.


Spiral rod shaped bacteria that cause food borne diseases,


Cocci shaped bacteria that cause urinary tract infection.


Bacteria that cause sexually transmitted disease.

Table 2. Flies are also concerned in transmission of:




Inflammation of the eye.


Bacillus anthracis causes bacterial infections in lungs and skin.


Mycobacterium cause infection in lungs.

Food poisoning

Food borne illness.

Parasitic worms

Parasites that live inside the host causing illness.

(Cohen et al. 1991;Gr³bel and Cave 2004)

1.3. 1. A few common diseases caused by flies

Two methods of pathogenic transmission by flies are mechanical and biological transmission.

A few of the common diseases caused by flies are:



Enteric diseases

Transmitted indirectly. These diseases are transmitted mechanically and commonly by the house flies. Typhoid fever and cholera are the most common. Shigella, causes dysentery and diarrhoea.

African Trypanosomiasis (sleeping sickness)

Transmitted by the Tsetse Fly (salivary glands) in Africa.

American Trypanosomiasis (Chagas disease)

Muscle cells of the heart and digestive tract are invaded by trypanosome protozoa.


Disease is caused by the transmission of protozoa from the sand fly bites.


The disease is caused by the skipper fly. The eggs laid by the fly on the skin digs into the outer layer of the skin wounds.


The parasite, Entamoeba histolytica, found in uncooked meat causes chronic diarrhea.

Onchocerciasis (River blindness)

Microscopic nematode worm causes this disease. It is transmitted through the black fly bite.


Patients experience high fever. The disease is caused by the sand fly bite which transmits rickettsia organism.


Bacteria known as salmonella typhi causes high fever. It is transferred by the house fly from excrement.


Bacillus mycobacterium leprae is carried by flies from rotten food.

1.4. Maggots

Maggots are usually found in decaying bodies. They give an indication of time elapsed since the death and the place of the death, by identifying the stage of their lifecycle and species. Their DNA is used to identify their species. The size of house fly larvae is 10 - 20 mm. Histeridae (another insect family) feed on larvae. Thus, the lack of maggots would increase the estimated time of death. A few other species' of larvae are bred specifically for angling or as the food for pets such as reptiles or birds.

They are used in the production of some cheeses (casu marzu).

Necrotic wounds can also be cleaned out with the help of maggots.

Maggot debridement therapy is the use of disinfected and live fly larvae to promote the healing of wound by necrotic tissue cleaning. The maggot is introduced to the non healing tissue debridement of an animal or a human. (Jones and Wall 2008)

Dressing containing maggots are used to seal the non healing wound of the patient. The dressing is air permeable for the maggots to live. They are unable to reproduce in the dressing when they are satiated as they are immature. The length of the therapy depends on the severity of the debridement.


Figure 6. Patient after debriment and fasciectomy of the abdominal fascia, perineum, and scrotal fascia.


Figure 7. The placed Vitapads positioned on the wound. The tape on the edges will stop the maggots from escaping.


Figure 8. The same patient after one year

1.4.1. The mechanism of action

The maggots are used in the medical field for the three main reasons:


The wound containing the necrotic tissues is the ideal breeding area for bacteria leading to septicaemia, amputation and gangrene. The healing of the wound is stopped if the necrotic tissues have not been cleaned out. The surgeons can only debride the tissues they can see. This often results in the removal of healthy tissues along with the dead tissues causing pain in patient. If a tissue containing dead cells is not removed, bacteria may cause infection to the nearby healthy tissues, spreading it further. Therefore the maggots are used in specific areas where the surgeon is unable to remove the necrotic tissues. The healthy tissues are not damaged by the maggots. They consume with precise boundary. Maggots obtain nutrients by extracorporeal digestion. Proteolytic enzymes are used to liquefy dead tissue, which are later absorbed. (Jones and Wall 2008)


The wounds are harder to treat if they contain antibiotic resistant microbial strain. Although maggots are used to clean out the necrotic wounds, it contained secretion which could disinfect a bacterial infection. The infections can be life threatening. The secretion contained allantoin, phenylacetic acid, urea and calcium carbonate and proteolytic enzymes. The microbes that are resistant to these secretions are lysed and ingested within the maggots. A few of the pathogenic bacteria that are destroyed and inhibited by the maggots are MRSA, Gram-positive strains and group A and B streptococci. (van der Plas et al. 2007)

Wound healing

Epidermal growth factor and IL-6 are amplified by the maggot secretion. The growth of the fibroblasts and chondrocytes are also stimulated by the secretions. Moreover, wound exodus and formation of granulation tissue are also stimulated. (Li et al. 2009)

1.4.2. Limitations

Only moist wounds are suited to maggot therapy. Adequate oxygen supply is also necessary. Although dry wounds can be moistened with saline soaks, it does not provide a good feeding environment for the maggots. Maggots often have a short life span which restricts its long-term use. Patients may also find them distasteful or disgusting. Therefore polymer bags are used to hide them from other's site. (Li et al. 2009)

The three types of flies that are studied in our project are:

1.5. House fly

The most common type of flies found in most homes is the houseflies also known as Musca domestica. These flies are considered a pest as it carries the common diseases.

Figure 9. An adult housefly

Houseflies feed on sputum, feces, and humid decaying organic materials. They can only take in foods in liquid form. Therefore, they use their saliva to predigest the solid food which is later sucked in. House flies also regurgitate certain digested food and take it again to its abdomen.

Mechanical transmission of organisms on flies:

"Parasitic diseases: Cysts of protozoa e.g. Entamoeba histolytica, Giardia lamblia and eggs of helminths e.g.:Ascaris lumbricoides,Trichuros trichura, Haemenolypes nana, Enterobius vermicularis". (F÷rster et al. 2009)

Viruses: Enteroviruses: Poliomyelitis, infective hepatitis (A & E). etc

"Bacterial diseases: Typhoid, cholera, dysentery, pyogenic cocci, etc. House flies have been confirmed to be carriers of Campylobacter and E. coli O157:H7 using Polymerase Chain Reaction". (Ahmad et al. 2007)

Polymerase chain reaction can also be used to identify the pathogenic bacteria contained in the house fly. (Ahmad et al. 2007)

1.6. Greenbottle fly

The greenbottle fly comes from the species of blowfly, in the genera Lucilia and Phaenicia. The common species of greenbottle are Lucilia cuprina, Lucilia caesar, Lucilia coeruleiviridis, and Lucilia illustris. The maggots of the greenbottle fly feed only on dead tissues and not the living cells. Therefore the larvae of greenbottle fly are used in maggot therapy. (Graczyk et al. 2001)

Figure 10. An adult greenbottle fly

1.7. Bluebottle fly

The bluebottle fly is another type of blow fly known as Calliphora vomitoria. They are half an inch larger than the house flies. The rotting materials attract the adult bluebottle flies. These flies play an important role in ecological system as they feed on dead or dying materials. It is usually the female flies that enter indoors. (Stevens 2003)

Figure 11. An adult bluebottle fly

1.8. The microbiology of maggots used in angling

1.8.1. Pinkies

As its name suggest this maggot is pink in colour. Pinkies are the larvae of the green bottle fly, close to its relative the blue bottle and are about two thirds the size. They are usually about 15 mm long and have the same feed sack as maggots. Like maggots pinkies come in different colours amongst which the red maggot and the natural white are the most common but with one major exception, the fluorescent pinkie, a pink/red colour and usually devastating particularly in the winter. Fluorescent pinkies are very good in cold weather. Pinkies are good as hookbait for small fish at all times. However,being smaller than large whites they are less likely to overfeed the fish. Also being lively, pinkies tend to burrow out of sight into the bottom when fed into the swim. Pinkies are small, light maggots best suited to canals, still waters and slow-moving rivers as they tend to fall slowly in the water and fast flowing water will wash them away. (Adams and Hall 2003)


Figure 12. Pinkies are the larvae of greenbottle fly.

Storage - This is totally dependent on the age of the maggot. Maggots can be stored for 10-15 days provided they are kept cool, as cool environment slows down the natural ageing and development of the maggot in to its chrysalis state. Pinkies are sold in either saw dust or maize to keep them clean and in the best state possible. To keep maggots for any length of time it is advisable to change the sawdust or maize regularly. Pinkies kept for ages in the fridge can be going strong after 2 or even 3 weeks. (Adams and Hall 2003)

Hooking - The pinkie should be hooked in the same way that you would hook the white maggot, through the bearded end. As the Pinkie is small in size it stands to reason that the hooks need to be smaller too. Again when hooking the pinkie the maggot should remain lively and no fluid should be released. (Adams and Hall 2003)

1.8.2. Squatts

The squat or feeder as it is commonly known is the smallest of the maggot family and are the larvae of the housefly. The mature larva is usually 3 to 9 mm in length, creamy whitish in colour, cylindrical but has a tapering head. The head consists a pair of dark hooks. These legless maggots emerge from the eggs during summers within 8 to 20 hours, and they immediately feed on the wastes the eggs were laid on. The fully grown maggots are 12mm long n are greasy on surface. The fully grown maggots move up to the cold dry place for their transformation into pupal phase. (Hou et al. 2007)

They are usually used as loose feed and like the Pinkie are more suitable to still or slow moving water as they sink very slowly. The squat is rarely used as hook bait but can be if needed. The squat is a slow moving sluggish maggot that displays little activity when it is on the bed of the water. For this reason they are an excellent fish holding bait and are a good choice when used with ground bait. (Hou et al. 2007)


Figure 13. Squatts are the larvae of housefly.

Storage - Squats are usually sold in damp sand which helps to stop the maggot from drying out. Unfortunately the squat will not keep for more than a few days so it's a good idea not to buy too many at any one time. (Hou et al. 2007)

Hooking - These are not usually used as hook baits but it stands to reason that due their size they will need a small hook to hook them effectively. The squat when hooked should be hooked in the same way that you would hook the white maggot, through the bearded end.

1.8.3. Calliphora larvae

The white maggot is the larvae of the common Blue Bottle and is the largest of the maggot family. As soon as, the larvae emerge from their eggs, they begin to consume on the surrounding dead or decomposing organic material. Once they are fully grown within a period of a week, they leave the carrion.  (Stevens 2003)

Most insect larvae have organs called stemmata which contain the photoreceptors, however, these appear to be absent in maggots. There are a number of structures at the front end of a maggot that have at one time or another been suggested to be the site of photoreception. These include chemoreceptors and even the imaginal discs that are destined to become the compound eyes of the adult fly. (Stevens 2003)

Good quality maggots will be lively and soft to the touch. They will have a black spot under the skin which is an indication of having recently fed (the larger the spot the younger the maggot). Maggots that are slow moving or firm to the touch are older and will therefore turn in to casters much sooner. (Stevens 2003)


Figure 14. Calliphora are the larvae of bluebottle fly.

Storage - This is totally dependent on the age of the maggot. Keeping the maggot cool slows down the natural ageing and development of the maggot in to its chrysalis state and can therefore be kept for 10-15 days. When kept in warm conditions they last not more than 2 days. Maggots that have been left in warm conditions become sweaty and will eventually die. Sweaty maggots stink due to which they will not be attractive to fishes. (Stevens 2003)

Hooking - As a general rule of thumb, small hooks should be used when hooking maggots. When the point of the hook is pressed across the beard of the maggot, the maggot should remain lively avoiding the release of fluids.

1.8. Campylobacter Species

The genus Campylobacter is a gram negative; microearophilic curve shaped rods that can cause certain diseases such as Campylobacteriosis in both human and particular animals via infection and contamination from the genus itself. Most common species in human pathogens are Campylobacter jejuni and C. Coli and the least common ones are C. Lari, C. Hyointestinals, and C. Fetus. A very high amount of Campylobacter bacteria is detectable in the faeces of individual suffering from acute campylobacteriosis due to developing gastroenteritis. At this stage the Campylobacter could easily be detected and separated from the faeces sample using selective agar plates, however at the later stage is more difficult to detect the bacteria in that way as the number of bacteria decreases in the samples due to the increase of the number of dead or injured cells interfering with microbial flora (Figure 15).

C:\Users\User\Desktop\Campylobacter\Campylobacter jejuni.jpg

Figure 15. campylobacter(gram -ve curve shaped rods.

This bacteria cause food born infections from mild to severe diarrhoea. This is a big concern in angling industry as the fishermen who eat food after handling the contaminated larva without washing their hands. Therefore they develop illnesses such as food poisoning and diarrheal illnesses.